(1) Field of the Invention
The present invention relates to a semiconductor laser capable of generating an ultrashort light pulse train with an ultrahigh repetition rate, which is usable in optical communications and optical information processing.
(2) Description of the Related Art
In recent years, there has been an increasing demand in the fields of optical communications and optical information processing for basic technologies to enable the generation of pulse trains having ultrahigh repetition rates which range from several tens of gigahertz to more than 100 gigahertz. One type of light oscillator which generates high-speed light pulses is a mode-locked semiconductor laser having a two- or three-section configuration. It has been reported that, in this device, it has been possible to apply reverse bias to one section, which is separated by means of electrodes, resulting in operation in the saturable absorption region, thereby enabling achievement of self-excited pulse oscillations having a repetition frequency of 100 GHz and above. This technology has been described in the literature by, for example, Y. K. Chen (paper in the IEEE Journal of Quantum Electronics, Vol. 28, No. 10, pages 2176 to 2185).